Chemical nickel plating



Oct. 11, 1960 A. H. nu ROSE 2,955,959

CHEMICAL NICKEL PLATING Fil-ed Sept. 22, 1958 Q HEATINDUCING u ALT ERNATING CURRENT ELECTRIC HEATER mom. 2 NICKEL PLATING OBJECT PLATlNG SSOLUTION TO BE gnunou 4 PLATED 5A FIG. 1 FIG. 2

STEAM SPENT STEAM NlCKEL NICKEL PLATING PREPEEgED PLATIN6 gOLUTION Q? B E gOLUTION OBJECT TO BE PLATED PLATED FIG.3 PI6.4\

ARTHUR H. DUROSE, INVENTOR.

BY M amemm Patented Oct. 11, 1960 CI'IENHCAL NICKEL PLATHNG Arthur H. Du Rose, 107 E. 292 St., Euclid 23, Ohio Filed Sept. 22, 1958, Ser. No. 762,249

8 Claims. (Cl. 117- 113) The present invention relates to processes of chemical nickel plating.

Methods of nickel plating which do not depend upon the passage of an electric current through the plating solution have been known for many years. Such processes are described, for example, in US. Patent No. 455,230, issued in 1891, and in U.S. Patent No. 1,207,218, issued in 1916. More recently, such processes have come into commercial use and particularly those of the type described in US. Patent No. 2,658,839.

In these commercial processes, the usual mode of operation is to maintain a chemical plating solution at an elevated temperature, close to the boiling point of the solution, and to immerse the object to be coated in the solution for a period of time which is suitable for the thickness of deposit desired, ranging up to several hours. The process depends upon the reduction of nickel cations by hypophosphite anions in the presence of a catalyst, at temperatures near the boiling point of water. As is understood in the art, the catalyst is usually the object to be plated, though in some instances a non-catalytic object may be plated by initiating the plating reaction in various Ways as discussed below. These commercial processes are usually of a continuous-flow type, wherein the plating bath is a small, heated container, and the reserve solution is contained in a reservoir of larger capacity at a lower temperature. Additional reagent may be added during processing to the reservoir, to replenish the active agents in the solution which are used up during plating.

This two-tank system is used largely to overcome the difliculty encountered with undesired plating which tends to take place within the process equipment wherever the plating solution is present at elevated temperatures. Nevertheless, simply keeping the major part of the solution in the reservoir at a depressed temperature, does not completely overcome the problem, and the additional expedient of using tanks, conduits, and other equipment of nn-catalytic material, such as plastic, or which is glass-lined, also has been necessary. Even so, the plating reaction frequently is initiated on the non-catalytic materials used in the system, by specks of catalytic material, and once nickel plating begins, it continues, nickel being itself catalytic for the process. Thus, the problem has remained a serious one.

I have found that if the temperatures of the solutions used are kept below a certain critical point (about 185 F. in the case of the solutions which I have utilized), and if the workpiece itself is heated above such critical point, but its surface is kept below the boiling point of the solution, an excellent coating on the workpiece can be obtained while at the same time the problem of deposition of metal from the nickel solution onto the process equipment is largely avoided. This is because of the fact that in my process the major portion of the solution, all except a thin layer adjacent to the workpiece, may be kept below the critical temperature at which nickel deposition takes place at an appreciable rate, a temperature which I refer to herein as the critical point or the pre' cipitation temperature.

While my process is chiefly useful in those instances where the workpiece can be heated while in the solution, or can be repeatedly heated and dipped, it can, nevertheless, be used in an important number of industrial appli cations. For example, it may be used to plate the interior surfaces of tubing, 'a problem which was formerly very difiicult, and it may be used to plate hollow bodies of highly irregular shape, either externally or internally; and it has other uses which will be apparent from the following description.

In one method of practicing my invention I may "use a glass tank containing the plating solution, and heat -the solution in the tank by means of an external heating source. Two formulations of plating solution which may be used are as follows:

The quantities of reagents may, of course, be varied, within limits. Thus, satisfactory results could be obtained with nickel chloride present within the range of about 15 to grams per liter and sodium hypophosphite present within the range of about 5 to 50 grams per liter, while sodium citrate or sodium hydroxyacet-ate present in amounts from 5 to 60 grams per liter would be per missible. However, the preferred ranges for these substances are: nickel chloride 25 to 35 grams per liter, sodium hypophosphite 8 to 15 grams per liter, and sodium citrate or sodium hydroxyace'tate 5 to 15 grams per liter. The pH may vary from about 3.5 to 6 with a pH of around 4.5 to 5.5 being the most satisfactory.

As is well known in the art, other salts may be used to make up a plating bath containing nickel cations and hypophosphite anions, which would give similar results. Moreover, as is known in the art, the concentration of the various ingredients, within broad limits, has but little effect on the reaction, except perhaps for the speed at which it takes place, and except also that too high a concentration of hypophosphite tends to cause spontaneous decomposition to take place more readily.

With these solutions, the plating reaction which takes place is the following:

The reaction does not take place spontaneously, but only upon certain surfaces, which are, or can be made catalytic for the reaction. Such surfaces are copper, silver, gold, beryllium, boron, germanium, aluminum, thallium, silicon, carbon, vanadium, molybdenum, tungsten, chromium, selenium, tellurium, titanium, iron, cobalt, nickel, palladium, platinum and alloys thereof such as steel, brass and bronze. I will refer to such materials herein as basis materials. Nickel itself is a catalyst, so that the process is not self-limiting like the displacement method of plating and the thickness of the deposit is not limited.

There are various ways of inducing deposition on noncatalytic surfaces. Thus, Brenner and Riddell in Research Paper RF. 1835, volume 39, November 1947 of of a thin layer of catalytic non-catalytic material.

Talmey, US. Patent No; 2,658,839, states that some materials, non-catalytic by themselves, can be plated .by the use of iron as an initiator. that copper 'can be used as a basis',material by contacting it with an iron wire to initiate the plating reaction, after which the wire is removed. In this connection, it is of interest to note that I have found that 'copper. is a catalytic material if the solution is hot enough, and particularly if the amount of hypophosphite is increased somewhat.

Brenner, in U.S.,Paten,t No. 2,532,283, states that brass and bronze maybe plated by a chemical'process if they are given additional preplating treatment in the form of a,momentary.bright aciddip followedby a dip' for about one minute ina solution of 0.02 gram of palladium chloride j(PdCl and 20.0 grams ,of hydrochloric acid per-liter of solution. The vconcentration andlength of the palladium dip c'an'be varied inversely and when the solution is heated, can be'decreased. He states that objects of platinum and silver, when immersed in the plating bath require momentary contact with aluminum .to initiate the plating operation? Thus, it may be seen that my process is suitable for use on materials upon which the chemical plating reaction may be initiated by means which are knowninthejartgj" V 7 Using the solutions which Ihave mentioned, as-the reaction proceeds'the pH tends to drop, and for continued rapid deposition, additions of a dilute sodium hydroxide solution must be made. Sodium hypophosphite 'is'added only when needed, since a varying amount of loss of hypophosphite takes place in the presence of nickel salts by the following reaction: a

For example," he states material on the surface of the 4. Example IV A tank of solution A was placed in an induction furnace with a steel bar suspended in it. The solution was maintained at an average temperature of 130 F. for two hours, and no measurable amount of nickel was deposited. However, when the bar was heated by the induction eflect of the induction furnace for one hour, a 0.25 mil thickness of nickel was deposited on the steel bar.

The drawing is further illustrative of the foregoing examples, each figure of the drawing corresponding to its respectively numbered example.

Figure 1 illustrates the process performed in Example 1.

Figure ample 2.

Figure 3 illustrates the process performed in Example 3.

Figure 2 illustrates the process performed in Ex- 4 illustrates the process performed in Earample 4.

My proposed method is suitable for nickel plating'the interior of tubing or pipes. The'tubing, eitheriin a coil, or in the form of numerous straight courses connected by U-bends, and having an inlet andan outlet end,'can be enclosed in a heating chamber andplating solution passed through the tubing. Plating can then beaccomplished by maintaining'the heating chamber temperature near'the boiling point of the solution'forthe'appropriate length l of time for the thickness of plating desired. After plat- To make the process continuous, both reducting agent 7 and nickel salts must be replenished from time to time.

The following plating operations using the above solutions will serve as examples of the operation of my improved method:

Example I A length of steel wire (in this instancet35.5 mils in diameter) was immersed in a tank of solution A, the solution being held at 180 F. for 30 minutes. No discernible nickel deposit was produced. .-However,.when a 15 ampere current was passed through the wire from an alternating current source, thereby heating the Wire, a coating of nickel 0.5 mil in thickness was deposited on the wire in about 35 minutes. 7

Example 11 per hour on the external surface of the cylinder.

' Example Ill.

A coil of steel tubing having /1" outside diameter and a .03"wall thickness was immersed in solution B for one hour, during which time the solution was maintained at 164 F.' 'A deposit of 0.12 mils inthickness resulted. With steam at 232 F. passing through the tubing, a deposit 0.92 mil thick resulted, after one hour, on the external surface of the tubing. In this case, it may be noted that although the steam within the tubing was well above 'theboiling point of the plating solution, the solution did not boil because of the rapid convection which takes place during the process.

ing, the tubes or. pipes can be further processed; as by bending, or cutting to the desired lengths.

Similarly, by introducing plating solution into ahollow body'which is heated externally, thebody'may be in.-

ternally plated.

Massive bodies also can be plated by my method, by heating them, asin a furnace, then dipping into the solution, with repeated applications of heat, to'restore heat lost to the solution, and repeated dipping,'to the extent necessary, until the proper thickness of nickel is deposited;

I have found that the'optimum workpiece temperature,

in all cases, is a temperaturejust below that 'at' which the solution in contact with the workpiece begins to boil. If the temperature is too high, the solution will boil, and the workpiece will then be bathed withboth liquid and vapor alternately producing a very unsatisfactory plating result. It also appeared from my tests, that if the solution couldbekept below about F., the deposit of undesired nickel plating could be largely eliminated. t

My method is readily applicable to the type of industrial process in which the solution used is replenished continuously as it becomes depleted. This type of process has the advantage that, by providing for the regeneration of the solution, a high quality nickel plating of any reasonable desired thickness may be obtained. Such processes usually embody a small plating tank and a larger 'solution reservoir, with means for heating thesolution in the small plating tank, and frequently, means for cooling the solution as it goes to thelarge reservoir; Such systems usually also include various pumps, filters, "valves, etc. It is in this type of system that the problem of U117 wanted metal deposits is particularly serious, and necessi tates the complex apparatus providing for repeated heatingand cooling of solution as it flows through the system, and embodying glass-lined or plastic tanks, pipes, etc. By the application of my improved method, however, these expensive glass-lined and plastic systems may, inimany cases, be dispensed with; It still is desirable, although not absolutely necessary, to have a system comprising a small plating tank and a larger reservoir, 'since it is desrrable to maintain the plating solution at a temperature above room temperature. in the. plating tank. Actually, the process would work even if the main body of the solution were kept appreciably below room temperature, but there isno apparent economic reason for operating the system in this way. l

What I claim is:

1. A process comprising subjecting a surface of a workpiece to be coated with nickel to a body of chemical nickel plating solution comprising nickel cations and bypophosphite anions for time sufficient to produce a coat ing of desired thickness, said solution, except essentially a thin layer thereof closely adjacent to said workpiece surface being maintained at temperatures below the precipitating temperature thereof, said surface of said workpiece being maintained at temperatures above the precipitating temperature of said solution and below the boiling point thereof whereby a thin layer of solution adjacent said surface is at a temperature above the precipitating temperature of said solution and below the boiling point thereof, said surface of said workpiece being composed of a substance of the class consisting of copper, silver, gold, beryllium, boron, germanium, aluminum, thallium, silicon, carbon, vanadium, molybdenum, tungsten, chromium, selenium, tellurium, titanium, iron, cobalt, nickel, palladium, platinum and alloys thereof.

2. The process set forth in claim 1 werein said chemical nickel plating solution is an aqueous solution comprising a nickel salt Within the range from about 15 grams per liter to about 75 grams per liter and sodium hypophosphite within the range from about 5 grams per liter to about 50 grams per liter, and the pH of said solution is maintained within the range from about 3.5 to 6.0.

3. The process set forth in claim 1 wherein said body of chemical nickel plating solution is maintained at a temperature below 185 F. except a thin layer adjacent to said workpiece surface.

4. The process set forth in claim 1 wherein the said body of chemical nickel plating solution is maintained within a temperature range below 185 F. and the said solution is an aqueous solution comprising nickel chloride within the range from about 15 grams per liter to about 75 grams per liter, and sodium hypophosphite within the range from about 5 grams per liter to about 50 grams per liter, and the pH of said solution is maintained within the range from about 3.5 to 6.0.

5. In a nickel plating process of the chemical type, in which metallic nickel is deposited on a workpiece surface out of an aqueous chemical nickel plating solution near its boiling point, said solution comprising nickel cations and hypophospite anions, the process comprising the steps of immersing a workpiece of the class consisting of copper, silver, gold, beryllium, boron, germanium, aluminum, thallium, silicon, carbon, vanadium, molybdenum, tungsten, chromium, selenium, tellurium, titanium, iron, cobalt, nickel, palladium and platinum, and alloys thereof, in a body of said nickel cation-hypophosphite anion solution, the major part of said body of solution being maintained at a temperature below the precipitating temperature of said solution, heating the said workpiece surface to a temperature such that the portion of the said solution immediately adjacent said workpiece surface is slightly below the boiling point of said solution, and continuing said immersion and heating for a period of time required to produce the thickness of nickel plating desired, whereby nickel plating conditions occur in said body of solution substantially only at said workpiece surface.

6. The process set forth in claim 5 wherein said chemical nickel plating solution is an aqueous solution comprising a nickel salt within the range from about 15 grams per liter to about 75 grams per liter, and sodium hypophosphite within the range from about 5 grams per liter to about grams per liter, and the pH of said solution is maintained within the range from about 3.5 to 6.0.

7. The process set forth in claim 5 wherein the said body of chemical nickel plating solution is maintained within a temperature range below 185 F. and the said solution is an aqueous solution comprising nickel chloride within the range from about 15 grams per liter to about grams per liter, and sodium hypophosphite within the range from about 5 grams per liter to about 50 grams per liter, and the pH of said solution is maintained within the range from about 3.5 to 6.0.

8. Heating a surface of a workpiece to be nickel-coated while said surface is immersed in a body of chemical nickel plating solution comprising nickel cations and bypophosphite anions which is at a temperature below its precipitating temperature, said surface being at a temperature between the precipitating temperature of said solution and its boiling point, said workpiece surface being metallic and catalytic toward said solution, thereby to produce a deposit of nickel on said surface while said solution remains at a temperature below its precipitation temperature except for essentially thin layer closely adjacent to said workpiece surface.

Walker Dec. 14, 1869 Brenner et a1. Dec. 5, 1950 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2,955,959 October 11, 1960 Arthur H. Du Rose It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below.

In the grant, lines 1, 2 and 3, for "Arthur H. Du Rose, of Euclid, Ohio," read Arthur H. Du Rose, of Euclid, Ohio, assignor to The Harshaw Chemical Company, of Cleveland, Ohio, a corporation of Ohio, line 12, for '-"Arthur H. Du Rose, his heirs" read The Harshaw Chemical Company, its successors in the heading to the printed specification, line 3, for "Arthur H. Du Rose,

107 E. 202 St. Euclid 23, Ohio" read Arthur H, Du Rose, Euclid Ohio, assignor to The Harshaw Chemical Company, Cleveland Ohio, a corporation of Ohio Signed and sealed this 9th day of May 1961.,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

1. A PROCESS COMPRISING SUBJECTING A SURFACE OF A WORKPIECE TO BE COATED WITH NICKEL TO A BODY OF CHEMICAL NICKEL PLATING SOLUTION COMPRISING NICKEL CATIONS AND HYPOPHOSPHITE ANIONS FOR TIME SUFFICIENT TO PRODUCE A COATING OF DESIRED THICKNESS, SAID SOLUTION, EXCEPT ESSENTIALLY A THIN LAYER THEREOF CLOSELY ADJACENT TO SAID WORKPIECE SURFACE BEING MAINTAINED AT TEMPERATURES BELOW THE PRECIPITATING TEMPERATURE THEREOF, SAID SURFACE OF SAID WORKPIECE BEING MAINTAINED AT TEMPERATURES ABOVE THE PRECIPITATING TEMPERATURE OF SAID SOLUTION AND BELOW THE BOILING POINT THEREOF WHEREBY A THIN LAYER OF SOLUTION ADJACENT SAID SURFACE IS AT A TEMPERATURE ABOVE THE PRECIPITATING TEMPERATURE OF SAID SOLUTION AND BELOW THE BOILING POINT THEREOF, SAID SURFACE OF SAID WORKPIECE BEING COMPOSED OF A SUBSTANCE OF THE CLASS CONSISTING OF COPPER, SILVER, GOLD, BERYLLIUM, BORON, GERNAMIUM, ALUMINUM, THALLIUM, SILICON, CARBON, VANADIUM, MOLUBEDENUM, TUNGSTEN, CHROMIUM, SELENIUM, TELLURIUM, TITANIUM, IRON, COBALT, NICKEL, PALLADIUM, PLATINUM AND ALLOYS THEREOF. 